PAW LOW'S RESEARCHES. 497 



This reflex secretion only occurred when meat was eaten 

 and not when water, milk, or soup was given to the dog. 

 It is interesting to note that in many cases merely showing 

 the meat to the hungry dog would cause a secretion of 

 gastric juice, and that this secretion stopped as soon as the 

 dog recognised that he was being teased, and was not in- 

 tended to have the meat — an instance of the influence of 

 psychical events on the processes of digestion, of which we 

 have so many examples in our daily life. 



Here at last we have a means of obtaining a perfectly 

 pure gastric juice free from all admixtures with foreign 

 substances, such as food or saliva. The characters of this 

 pure gastric juice have been investigated more nearly by 

 Pawlow's pupil, Schoumow-Simanowsky. When secreted 

 it is perfectly clear and colourless, its sp. gr. varying from 

 1003 to 10,059. It is feebly dextrorotatory, gives no 

 biuret reaction, but gives the ordinary reactions (xantho- 

 proteic, etc.) for proteids. It inverts cane-sugar and is 

 strongly proteolytic. Its total solids vary from '292 to *6o 

 per cent. ; ash from '10 to '160 per cent. It is strongly 

 acid, the acid varying between '46 and "58 per cent. HC1. 



An extremely interesting point about this juice is that, 

 when cooled to o°, it deposits a fine powdery precipitate 

 which appears to consist of pure pepsin. When this precipi- 

 tate has fallen to the bottom, it is found that the acidity of 

 the fluid increases from the top to the bottom. Thus in one 

 case the upper layer contained '45 per cent. HC1, while a 

 sample from the lower layer contained '63 per cent. HC1. 

 In another case, the upper layer contained -4 per cent., the 

 middle "45 per cent., and the lower layer it per cent. 

 HC1. This increase of acidity in the lower layers shows 

 that the acid must be in a condition of loose combination 

 with the pepsin, and is therefore carried down with this 

 body when it is precipitated by means of cold. 



By treating large amounts of gastric juice, it is possible 

 to obtain sufficient of this cold precipitate for analysis. The 

 precipitate forms an extremely light powder which gives all 

 the proteid reactions. Even after thorough washing it pre- 

 sents a markedly acid reaction, and in solution gives the tests 



